You've been in non-vegan situations for most of your life without any problems, right? It's not until you went vegan that it got trickier.
Don't expose yourself to non-veganism by being non-vegan!
The best way I know to increase your confidence in non-vegan situations... Whether it's the business dinner, the family gathering, or whatever else you've got going on, it's easy to get overwhelmed when you're the only vegan surrounded by meat eaters who, frankly, just don't understand you at all. Wouldn't it be awesome to be able to handle those scenarios with ease?
Before we even get to that, I should clarify. After all, you've been in non-vegan situations for most of your life without any problems, right? It's not until you went vegan that it got trickier. So really, this is about building confidence in non-vegan situations "as a vegan," which is an important distinction, really.
Here's how not to do it, but it's a valid option and one that I've caught myself following from time to time: you can simply avoid all non-vegan situations. Move to a big city if you're not already in one, make vegan friends, go to vegan restaurants, have vegan potlucks, shop in vegan stores, convert your family to veganism or else limit contact, add various other progressively extreme options, and boom! A happy, if sheltered, vegan life. Confidence doesn't come up because it's never needed.
I'm not even kidding about that option. People do it. Sometimes it's by choice, and sometimes it's just something that evolves, but it's completely possible.
I suspect, rather strongly, that people who do this are more likely to fail. Living in a vegan utopia sounds great (and I'm sure it is,) but you're going to end up relying on that too much, and guess what? The rest of the world isn't vegan, and at some point there's going to be an intersection of those two worlds and it's not going to be pretty if you're not ready for it. If that intersection happens as a result of something that's out of your control, it gets even worse because you're feeling helpless to begin with.
So here's the alternative: build your confidence by exposing yourself to progressively difficult non-vegan social situations (when I say non-vegan, I mean the other people aren't vegan, but you still are. Don't expose yourself to non-veganism by being non-vegan! This would sound trite and obvious if I just said "you need to get yourself into more non-vegan situations" so please pay attention to the "progressively difficult" part.
Without that specifier, it boils down to "practice practice practice," and the reality, which most people miss in their fervor for the "all you need is 10,000 hours of practice and you'll be an expert" theory that keeps going around, is that if you keep doing the same things then yes, you'll get better at those things, but not by a lot, and it'll just be those specific scenarios.
This is the part that sucks, but it's the only reliable way I can tell if I'm doing it right: I look to put myself in situations where I almost feel like throwing up. When that happens, I know I'm out of my comfort zone. And it is, quite honestly, the worst feeling ever, but I can get through it because I know there's a good chance I'm going to get better at it.
After a few times, I find that I don't feel quite so sick anymore. That's the sign that the practice is done and it's time to move on to a new, more difficult challenge.
Here are a few examples from my own life that happened just recently (I've got a few videos planned about them, but I might not focus on the comfort zone part as much):
I went to a catered dinner and didn't tell anyone I was vegan until the morning of the event. Normally I advise giving a few days notice, but I wanted to see what happened if I became a bit of a nuisance, and it meant being prepared to sip ice water all night in front of an elaborate, but empty place setting (it worked out, luckily.) In this case, I was uncomfortable with the last-minute ask, and while I avoided the disaster scenario in the evening, there was a minor bit of discomfort being the "special kid" at the table - which I've now done a few times and it's gotten easier and easier, so I'm not counting it as an exercise anymore.
I also invited myself to lunch with some new business contacts at a seminar. This was a snap decision, to a restaurant of their choosing that I don't usually eat at, so I wasn't 100% familiar with the menu but remembered the pickings to be slim. Unlike what I normally advise, there was no call-ahead, no advance menu planning, and I was trying to make a positive first impression on these guys, so a 10 minute deep read of the menu or asking the waiter 100 questions wasn't a good option. You know what? I don't think they even noticed I was vegan.
Did I get lucky in both these cases? Sure. You know what? Luck happens more than you think. Here's the big thing though: a year ago, I probably would have rather died than expose myself to these issues, or at the very least I would have skipped out on some hyge opportunities, and mentally associated my veganism with limitations instead of the many positives it's brought me.
So here's the contradiction, if you've followed my work for any length of time: I usually advise people to structure their lives as much as possible so you're actually in that "vegan utopia" scenario as much as possible, which sounds a lot like the "do this and you'll probably fail" option I outlined earlier.
Here's the trick: you need a safe home base. Going out of your comfort zone is, by definition, uncomfortable. Frankly, it sucks, or at least the initial process (the rewards are more than worth it, trust me.) As with most things, the growth is in the recovery, so you want to have that zone of safety to live in for much of the time, but you also want to plan "expeditions" into the big bad non-vegan world on a regular basis.
Ultimately, you need to find a balance that works for you. If you feel like you're going to throw up all the time, that's going to stress you out beyond belief. Yes, you might end up becoming a supervegan, but you might also end up in therapy :) Figure out a happy balance, and then push yourself a little outside of it from time to time.
And of course, going out of the comfort zone works in a lot of other scenarios, but we've just covered confidence today. You've probably got some examples from your past already (learning to drive is an easy one) where something used to freak you out and you now handle it as a matter of routine, but if you apply this strategy for a few months, even just once a week, you'll get a lot more examples without even consciously realizing it.